1. Technical Field
The present disclosure relates to an extinguishing unit for a molded case circuit breaker, and more particularly, to an extinguishing unit for a molded case circuit breaker that has grids double-arranged in an extinguishing part to improve arc extinguishing performance.
2. Description of the Related Art
In general, a molded case circuit breaker (MCCB) is an electric device that protects circuits and loads by automatically shutting off the circuits in the event of electrical overload or short circuit.
FIG. 1 is a longitudinal sectional view showing a molded case circuit breaker according to the prior art. The MCCB according to the prior art includes a fixed contact arm 2a and a movable contact arm 2b, which constitute a contact portion provided in a case 1 formed of an insulation material to connect or disconnect a circuit between a power source side and a load side, an opening and closing mechanism 3 for providing a power for rotating the movable contact arm 2b, an extinguishing part 4 provided to extinguish an arc generated when a fault current is interrupted, and a detection mechanism 5 for detecting an abnormal current.
An arc is generated between the fixed contact arm 2a and the movable contact arm 2b when flow of a fault current is interrupted by separating the movable contact arm 2b from the fixed contact arm 2a. The intensity of the arc is proportional to the magnitude of the current. The arc is generated when a gas in the atmosphere instantly reaches a plasma state. The temperature at the arc center reaches 8,000 to 12,000° C. and the arc has an explosive expansion pressure. Such arc melts and consumes the contact arms, and deteriorates or destroys the insulation material. Accordingly, persistence of the arc significantly affects the performance of the MCCB. Therefore, the arc should be quickly interrupted and extinguished in the extinguishing part 4 and be discharged from the extinguishing part 4.
As described above, in an MCCB, triggering a trip operation in the event of a fault current and extinguishing and discharging the arc generated according to the current are core operations in protecting the product, the loads and the cable by cutting off the fault current, and are directly related to performance of the circuit breaker.
FIGS. 2 and 3 are partially detailed views of an arc extinguishing part. FIG. 2 is a side view of an arc extinguishing part shown along with a contact portion, and FIG. 3 is a perspective view of an arc extinguishing part.
The movable contact arm 2b is pivotably coupled to a shaft 6, which is rotated by the power transferred from the opening and closing mechanism 3. The contact portion where the fixed contact of the fixed contact arm 2a meets the movable contact of the movable contact arm 2b is disposed inside the side plates of the extinguishing part 4.
The extinguishing unit, mainly used for the arc extinguishing part of the MCCB, is a cold cathode type extinguishing chamber using a metal plate. The extinguishing unit is formed by perpendicularly arranging grids 4b, which are made of a steel plate having a V-shaped groove and spaced an appropriate distance from each other, with respect to an arc generation path. When the contact arms 2a and 2b are separated and an arc is generated, the arc moves to the grids 4b within the side plates 4a. The arc is cooled by the grids 4b and divided into short arcs in between the grids 4b, whereby the arc voltage is increased and the current is reduced. In addition, an extinguish gas generated in the insulation plate (not shown) constituting the extinguishing part increases the internal pressure of the case, compresses the arc at a high pressure and suppresses release of free electrons, thereby quickly extinguishing the arc and recovering the inter-pole voltage.
As described above, minimizing consumption of the contact between the contact arms due to an arc and suppressing molten missiles by quickly extinguishing the arc in the event of short circuit is an important factor in implementing the basic function of the MCCB.
The MCCB according to the prior art has a current blocking capability of interrupting a fault current in a short time by suppressing the short-circuit current by increasing an arc voltage generated during short circuit breakdown. However, if the arc generated between the contacts in the short circuit breakdown is not completely cooled down by the grids to be extinguished, the grids in the extinguishing chamber may be damaged or even collapsed, malfunction occur due to missiles produced by melting of the grids, and the consumed amount of the contact may increase. Furthermore, while the MCCB becomes compact, an increased breaker capacity is required. Therefore, there is a need for enhancement of the extinguishing performance of the MCCB.